Comparative evaluation of physiochemical properties of a solid fuel derived from adansonia digitata trunk using torrefaction

Abstract

The effect of temperature on the physiochemical characteristics of a solid fuel or biocoal derived from the dried trunk of Adansonia digitata (Baobab) was studied using torrefaction processes. The chemical composition of the solid fuel or char obtained by wet (HTC) and dry torrefaction processes were determined by elemental and thermogravimetric (TGA) analyses. The Brunauer-Emmett-Teller (BET) surface area analyzer measured the porous texture and surface area of the prepared samples. The changes in the surface morphology and crystallinity of the prepared samples were evaluated by field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The torrefaction process successfully improved the energy content from 16.8 MJ/kg to 22.0 MJ/kg, which was evidently higher than the starting precursors. The maximum energy yield obtained was 90.0% using dry torrefaction at 250 °C. The energy densification ratio was also higher for the char produced by the dry torrefaction process. However, the char produced by the HTC process at 250 °C showed the highest surface area. The pore diameter was higher for HTC-char produced at the same temperature. Overall the results revealed that the torrefaction of lignocellulosic biomass is beneficial for upgrading the fuel quality and energy densification of char residues.